The invention relates to an apparatus for the control of the rotational speed of a driving-unit for a yarn windings storage drum, as customarily used with devices for storing and delivering yarns in textile machines.
Such an apparatus is particularly useful for machines, which during the progress of the manufacturing process show continuously or even only intermittently an irregular consumption of yarn, as occurs for instance with knitting or hosiery machines, which inter alia knit special patterns of knitwear or rely on jacquard systems, or operate according to stripe patterns, or with shuttle systems or systems which knit plush. The apparatus is also applicable to straight knitting machines or to looms with so-called thread shots.
It is an object of the invention to eliminate the tension differences which appear in the unwinding of yarn from a yarn bobbin as a consequence of the variation of the bobbin diameter and yarn speed. A further object of the invention is to at least to eliminate or simplify the conventional means for guiding, braking and controlling the yarn to minimize the unwanted yarn tension increasing effect.
By inserting such an apparatus in between the yarn bobbin and the knitting point, it is aimed at obtaining principally a uniform knitwear as to length and knitting quality (for instance the pattern of the stitches) and at obtaining a higher efficiency of the machine as a consequence of less disturbances, for instance caused by yarn breakings.
It is already known in circular knitting machines to rely on the method which provides that all yarns to be processed are supplied through yarn delivery devices, which have additionally the task to stop the machine when a yarn break occurs, so as to avoid or at least to strongly limit the damaging of needles and cylinders which otherwise would inevitably occur. The yarn winding serves here as an additional reserve. However the problems in such circular knitting machines are much simpler, at least with the knitting of so-called straight or approximately straight knitwear, if compared with the requirements existing in a comparable apparatus for supplying the yarn in connection with an irregular, i.e. intermittent, yarn consumption, as occurs in the textile machines of the kind above mentioned.
In such known devices for circular knitting machines, as a consequence of the synchronism between the movement of the machine cylinder and the consumption of the yarn of each single knitting point, it is possible to supply the yarn, through relatively simple mechanical means, in correct quantities. Practically, such yarn supply devices are directly driven, mostly in a synchronous way through a continuously adjustable gear device, which is controlled through a toothed belt or the like by the machine cylinder.
For obvious reasons such a yarn supply device is not applicable to textile machines with an intermittent yarn consumption. The sudden variations of the speeds of the yarn which occur with such machines while the cylinder is per se constantly operated cannot be performed by any yarn bobbin of a conventional yarn supplying device. Accordingly, in this complex field so-called storage drums are used in order to solve the problems which are posed.
Of these so-called yarn storage means, there are at least two main forms: one form provides for a yarn storage drum which is intermittently brought to a standstill, which has a rotating winding means which winds up the yarn on the storage drum; the other form provides only for a rotating storage drum, on which the yarn is wound.
The common feature of such embodiments is the principle of the winding of the yarn on a storage drum, so as to render ready a sufficiently large reserve of yarn, while sensitive means ascertain in due time when the yarn reserve has to be replenished as a consequence of the unwinding requested by the textile machine. A further common feature is the fact that collector-free three-phase electrical motors are provided for their driving, which do not suffer from wear. This also means that as a difference from conventional yarn supplying devices for circular knitting machines, each yarn storage drum needs--in connection with its own driving--specially devised sensitive means, and furthermore there is a need for complex signal processing means with electronic control, in order to achieve a correct working operation.
For easily understandable reasons, the technical effort is thus considerable, if one wants to serve, in a textile machine as for instance a hosiery manufacturing automatic machine, each knitting point individually through a yarn storage means of the above kind. Already the complex mechanical construction above all in relation to yarn storage means with winding elements and standstill storage drum with three-phase motors fed by the main voltage render a correct and above all a convenient application practically impossible, even besides the high costs for installation and getting the main voltage, which such devices imply. Several devices for supplying yarns, with yarn storage means of small constructional requirements are known, such as those disclosed in U.S. Pat. No. 3,225,446 or German Patent B1 1 635 899; however such devices do not offer a real solution in particular for the optimal application in relation to the most differentiated kinds of yarns, as for instance the thinnest synthetic or natural fiber yarns, which include rubber or elastomer yarns on which synthetic or natural fiber yarns are wound around or the newer economically more convenient fiber whirling versions thereof. However also with conventional standard yarns, difficulties appear.
In fact a drawback of the device according to German patent D- PS 1 635 899 resides in the fact that the reserve winding wound on the winding drum always requires a relatively high number of windings before an oscillation of the arms under the action of the total friction resistance of the reserve winding on the winding drum starts to be operational. On the basis of the high total friction resistance which is needed to trigger the mechanical action and to eventually correctly control the driving of the winding drum, one practically always meets with undesirable over or under bobbining of the single windings in the reserve windings, which does not permit a uniform axial unwinding tension of the yarn. Other disadvantages are seen in the bulky construction, with deleterious inertial consequences. A further disadvantage is seen in the fact that the sensitive means to control the bobbin work on an on/off system, which does not permit a synchronous relationship between the unwinding status and the rewinding operation, etc.
A disadvantage of the device according to U.S. Pat. No. 3,225,446 is that the so-called optical electrical control of the reserve quantity is ineffective in practical use, and is biased by any light source, for instance by daylight, artificial illumination, machine illumination etc. or by volatile floating fiber particles, etc.
Other known devices as those taught by German Patent DE 28 49 388 or DE 26 51 857, are also complex and affected by fiber impurities always floating in the related environment.
Further known devices are shown in German published Patent applications DE 40 37 575 A1 and DE 39 04 807 A1, neither of which offer a simple solution to the problem inasmuch as they rely on massive storage drums, with the related problems of driving with collector-free three-phase motors. In fact, the larger the motor, the slower the reaction, and thus the larger the storage drum, and the reserve winding.
Another state-of-the-art device is known from EP-A-0192821.
DE-A-4 413 757 is considered to represent the closest prior art for the method of reflecting light operation, describing an apparatus (2) for controlling the rotation speed of a yarn windings storage drum (9,71), comprising a motor (4,72) for driving the drum; a scanning device (3) sensitive to the quantity of reserve windings (11,54,70) on the drum (9,71), whose sensed signals are processed by a signal processing unit (74) arranged between the scanning device (3) and the motor (4,72), the scanning device comprises a light source (27,45,50,59,85,86), whose optical path (40,60,63) is guided so as to impact the surface of storage windings (11,54,70) wound on the drum. A plurality of light guiding blocks (33,34) are connected with a related light source (27,43,50,59,85,86) for guiding a related plurality of light paths (40,60,63). A plurality of sensor means (28,44,62,87,88) are capable of receiving a related light path (42,63). The light guiding blocks and the sensor means are arranged on one side (or the other), in a radial direction, of the storage winding drum in FIG. 1. The light guiding block is provided with light passage preventing means (33) preventing the passage of light except through window means (32,41) facing the portion of the drum on which storage windings (11,54,70) are wound so that contiguous windings form a winding width which is capable of biasing the related light path before it reaches the related sensor means (28,44,62,87,88) which derives from such so biased light a signal to be processed by the signal processing unit (74), thereby controlling said motor (4,72). An obvious disadvantage of the here described scanning device is the fact that, although the optical path (40,60,63) is guided so as to impact the surface of storage windings (11,54,70) wound on the yarn storage drum (9,71), there is no direct physical contact between the said surface of the storage windings and the light guiding blocks (33,34). Particles of fibres, paraffin, dust and other material which are carried along with the ambient air amongst others and will thus deposit sooner or later on the window means (32,41) of said guiding blocks, and which will result in a malfunction or at least an unproper operation of the device.